Wetting agents for electroplating baths



This invention relates to additives for electroplating baths and to a process and a bath for electroplating making use of such additives. It more specifically relates to the addition of organic phosphoric acid derivatives to electroplating baths as wetting and porosity preventing agents.

It is known to add wetting agents to electroplating baths for the production of nickel, copper or zinc electroplates. These additives have the effect that the hydrogen which forms at the cathode during the electroplating process is released rapidly and as completely as possible. If the hydrogen remains on the cathode material for longer periods of time it causes an undesirable pore formation in the metal electroplates.

The prevention of pore formation is of great importance in the electroplating art in view of the desired corrosion resistance of the metal electroplates. Another task of the wetting agents is to prevent the electrophoretic deposition of small particles of impurities on the metal surfaces, because the corrosion resistance also suffers from the inclusion of foreign bodies in the electrodeposits.

Wetting agents have recently also been used in chromium baths. The effect achieved thereby is that the quantities of oxygen and hydrogen released in the chromium baths due to the poor current output do not escape in the form of fogs, but that instead a foam cover forms on the bath liquid. This measure prevents considerable losses in relatively expensive chromium bath liquid due to continuous removal of the fog by suction, so that in fit many instances the suction removal of the bath fog can be entirely omitted.

Despite the great number of known wetting agents the selection of operative substances for electroplating purposes is relatively small. Thus, alkyisulfonates, alkylsulfates and aralkylsulfonates or sulfates are preferably used in nickel electroplating baths, while in the field of acid and cyanide preliminary copper-plating alkyl-poly glycol others are employed. Perfluoro-alkylsulfonates are known to be stable wetting agents for chromium baths.

It is an object of this invention to provide Wetting agent additive compounds for electroplating baths which have a high degree of stability.

It is a further object to provide additive compounds which prevent vaporization and loss of the electroplating bath solution.

It is a further object to provide Wetting agents which may be used in acid, alkaline or cyanide electroplating baths to produce deposits of the Well known plating metals.

Another object is to provide electroplating processes and baths wherein electrodeposits may be obtained which are free from pores and inorganic impurities.

These and other objects of our invention will become apparent as the description thereof proceeds.

In a copending application, commonly assigned, Serial No. 807,286, was disclosed the use of acid alkyl and alkaryl phosphoric acid esters or their water-soluble salts as wetting agents in electroplating baths.

We have now found that halogen-free, acid phosphonic acid derivatives which contain at least one straight or 3,035,991 Patented May 22, 1962 n-Octyl-phosphonic acid-1 n-Dodecyl-phosphonic acid-l n-HeXadecyl-phosphonic acid-1 Z-Ethylhexyl-phosphonic acid-:1 n-Octylphosphonic acid-3 n-Decyl-phosphonic acid-4 or mixtures of such alkyl phosphonic acids in which the phosphonic acid group is attached to any desired carbon atom of the carbon chain,

Di-n-octyl-phosphonic acid Ethyl-n-decyl-phosphonic acid Methyl-n-undecylphosphonic acid Iso-octyl-n-dodecyl-phosphonic acid C'yclohexyl-phosphonic acid Methyl-cyclohexyl-phosphonic acids and the like, or their water-soluble alkali metal, ammonium, monoor dialkylamino, or monoand dial-kylolamino salts. These phosphonic acids and their production are well known.

Such compounds may be designated by the general formula:

[R-lZ wherein R represents a hydrocarbon radical as above defined and Z represents a phosphonic acid radical attached to the radical.

The wetting agents according to the present invention may be employed in known acid nickel, copper, zinc and chromium baths as well as in the alkaline electroplating baths and in particular in cyanide copper, zinc, cadmium, tin, silver, gold, brass or bronze baths. The wetting agents are added to these baths preferably in an amount of 0.01 to 5 grams per liter. The phosphonic acids undergo a remarkably low rate of consumption. They prevent the formation of annoying fogs by the formation of a foam cover, especially in chrome baths. They are inert toward brightening agents simultaneously employed and make it possible for the brightening effects of these substances to exert their full effect. *In comparison to the phosphoric acid esters of the principal patent application Serial No. 807,286, they possess an even greater stability in the above indicated baths.

The following specific examples are given to illustrate our invention and to enable persons skilled in the art to better understand and practice the invention and are not intended to be limitative.

Example I In a bright chrome plating bath containing 300 gm. per liter CrO 1 gm. per liter of n-docecylophosphonic acid-1 was dissolved. Upon chrome plating bright nickelplated objects in this bath at current densities of 15 amp./ dm. at 35 C. a foam cover of about 1 cm thickness was formed on the chrome baths, which completely prevented the formation of chromic acid fogs. The dodecyl-phosa phonic acid additive does not interfere with the bright chrome plating process. Bright, non-porous chrome deposits were formed. 7

Example II In a hard chrome bath containing 250 gm. per liter CrO 0.2 gm. per liter n-hexadecyl-phosphonic acid-1 and 2.5 gm. per liter cyclohexyl-phosphonic acid were dissolved. The hard chrome plate deposited on steel objects at 55 C. and 35 amp./dm. with this bath was full bright. Due to the mixture of organic phosphonic acids used in the bath, the occurrence of chromic acid fogs was completely suppressed due to the formation of the foam cover on the chrome bath.

While we have set forth certain specific examples and preferred modes of practice of our invention, it will be understood that the invention is not limited thereto and that various changes and modifications may be made in our invention without departing from the spirit of the disclosure or the scope of the appended claims.

We claim:

1. An electroplating bath for producing smooth, pore free electro-deposits of chromium comprising an aqueous solution of an inorganic salt of chromium and an additive compound having a structural formula as follows:

and salts thereof, wherein R is a hydrocarbon radical having at least 6 carbon atoms selected from the group consisting of alkyl and cycloalkyl radicals and Z is a 5. A process for producing smooth, pore free chromium electrodeposits which comprises depositing the chromium from a bath containing the metal in the form of an aqueous solution of an inorganic salt thereof, in the presence of an additive compound having a structural formula as follows:

[RElZ aqueous solution of an inorganic salt thereof, in the presence of 0.01 to 5 gm./liter of an additive compound having a structural formula as follows:

' and salts thereof, wherein R is a hydrocarbon radical phosphonic acid radical, said additive compound being having at least 6 carbon atoms selected from the group consisting of alkyl and cycloalkyl radicals and Z is a phosphonic acid radical.

7. The process of claim 6 wherein the additive compound is n-dodecyl phosphonicacid-l. 8. The process of claim 6 wherein the additive compound is n-hexadecyl phosphonic acid-1. 9. A method for preventing fogging and vapor losses of bath solution in the operation of chromium electroi plating baths which comprises adding to said bath 0.01

and salts thereof, wherein R is a hydrocarbon radical v to 5 gm./liter of an additive compound having a structural formula as follows:

and salts thereof, wherein R is a hydrocarbon radical having at least 6 carbon atoms selected from the group consisting of alkyl and cycloalkyl radicals and Z is a phosphonic acid radical.

References Cited in the file of this patent UNITED STATES PATENTS 2,893,932 Haas et al. July 7, 1959 

6. A PROCESS FOR PRODUCING SMOOTH, PORE FREE CHROMIUM ELECRODEPOSITS WHICH COMPRISES DEPOSITING THE METAL FROM A BATH CONTAINING THE CHROMIUM IN THE FORM OF AN AQUEOUS SOLUTION OF AN INORGANIC SALT THEREOF, IN THE PRESENCE OF 0.01 TO 5 GM./LITER OF AN ADDITIVE COMPOUND HAVING A STRUCTURAL FORMULA AS FOLLOWS: 